Ring binder mechanisms retain loose-leaf pages on rings. Ring binder mechanisms can be used in notebooks, files, briefcases, clipboards and other similar objects to give the object a loose-leaf page retaining function. A conventional ring binder mechanism has rings formed by ring members that are selectively moveable to open the rings to add and/or remove loose leaf pages and close the rings to retain loose-leaf pages on the rings. The ring members are commonly mounted on adjoining hinge plates supported by a housing for pivoting movement between open and closed positions. The undeformed housing is slightly narrower than the combined width of the hinge plates such that the housing applies a spring force that biases the ring members against movement toward the open position when they are in the closed position. If this spring force is strong, there is a risk that a user could be injured by getting a finger pinched between the ring members as the housing causes them to snap shut during closing. Thus, it is desirable to design the housing so it exerts a relatively light spring force on the ring members to reduce the risk of injury to users.
However, the absence of a strong biasing force holding the ring members in the closed position increases the risk that the rings will inadvertently open (e.g., if the ring mechanism is accidentally dropped) and fail to retain loose-leaf pages. One way to reduce the risk the rings will inadvertently open is to provide a locking system that blocks pivoting movement of the ring members from the closed position to the open position. It is desirable for the locking system to automatically lock the rings closed when the rings are moved to the closed position. It is also desirable to be able to unlock and open the rings in a single step to make the ring mechanism convenient to use.